Moment tensors of acoustic emissions in shear faulting under plane-strain compression     

Fernanda C. S. Carvalho  Joseph F. Labuz   《Tectonophysics》2002,356(1-3)

The study of localized failure under controlled conditions can be accomplished within a laboratory setting with the University of Minnesota plane-strain compression apparatus. The device provides an opportunity to observe shear faulting and to compare displacements from acoustic emission (AE) sources with global measurements. A biaxial compression test on a sandstone specimen was performed with monitoring of AE. The plane-strain test showed that the shear fault was not formed until after peak load. Compaction of the shear fault was observed from the axial and lateral measurements of displacement and the orientation of the failure plane. The AE events were modeled as displacement discontinuities. The complicated deconvolution process for the transducer transfer function was eliminated by using a simplified calibration procedure. The sources of the postpeak events were characterized as being caused predominantly by slip in the direction of the global failure plane, although components of displacement associated with closing were identified. To provide an order of magnitude estimate of the slip, the field observation of a 10⁻⁴ strain drop over the seismic area was assumed. The tangential displacement from 110 AE events was estimated to be 0.01 mm. During the same period of time, the displacement along the shear fault from global measurements was 0.03 mm.  相似文献   

A technique for the molecular genetic analysis of Daphnia resting eggs from sub-recent lake sediments     

Vicky A. Reid  Gary R. Carvalho  D. Glen George  Huw I. Griffiths 《Journal of Paleolimnology》2002,27(4):481-486

The Polymerase Chain Reaction (PCR) was employed to facilitategenetic analyses of Daphnia ephippial egg banks fromsediment sequences from lakes Windermere and Esthwaite in the English LakeDistrict, UK. We present a robust DNA extraction technique for resting eggs andan account of genetic characterisation of dated resting eggs from sedimentcores using both mitochondrial and nuclear DNA markers. We also providepreliminary results from genetic analysis of egg banks preserved in shortsediment cores. PCR was employed to facilitategenetic analyses of Daphnia ephippial egg banks collected from both lakes. Thelong-term environmental data available from lake records can provide a backdropagainst which molecular genetic-environmental interactions over time can beexamined, providing a technique for direct assessments of population responseto environmental change in paleolimnological studies of biodiversityhistory.  相似文献   

Mapping oil spill environmental sensitivity in Cardoso Island State Park and surroundings areas, São Paulo, Brazil     

Arthur Wieczorek  Dimas Dias-Brito  Joo Carlos Carvalho Milanelli 《Ocean & Coastal Management》2007,50(11-12):872-886

This study presents an environmental oil spill sensitivity map of Cardoso Island State Park, located in São Paulo state, Brazil, including some of its surrounding areas. This map was designed following the procedures determined by the Brazilian Federal Environment Organ (Ministry of the Environment), which separates coastal habitats in different littoral sensitivity indexes (LSI) to oil spills. We have also analysed some seasonal variations in morphologic and textural parameters at the local marine beaches that could affect their sensitivity, having found that they are more sensitive during summer due to a wider foreshore zone during these periods. Local most sensitive habitats are estuarine mangroves (LSI 10) and estuarine mud banks (LSI 9). Marine beaches were ranked LSI 3, and littoral rocky shores were subdivided in exposed flat rocky shores (LSI 1), boulder rocky shores (LSI 6) and sheltered rocky shores (LSI 8). Due to the elevated sensitivity of an estuarine system in the area, we considered necessary the installation of an Environmental Emergency Centre and the design of an emergency plan for the region in case of an accident resulting in oil spills within its vicinities.  相似文献   

Molecular composition and chemosystematic aspects of Cretaceous amber from the Amazonas,Araripe and Recôncavo basins,Brazil     

Ricardo Pereira  Ismar de Souza Carvalho  Bernd R.T. Simoneit  Débora de Almeida Azevedo 《Organic Geochemistry》2009,40(8):863-875

Amber occurrences in Brazil are rare. In this regard, the molecular composition of three such fossil resin samples from Brazilian Cretaceous sedimentary basins has been analyzed to determine the botanical origin of the resins. The samples were collected from the Amazonas (Alter do Chão Formation), Araripe (Santana Formation, Crato Member) and Recôncavo (Maracangalha Formation, Caruaçu Member) basins. The mono-, sesqui- and diterpenoids in the extracts were used as chemosystematic markers when compared with terpenoids in extant conifers. The compounds were mainly diterpenoids and their degradation products from the labdane, podocarpane, pimarane and isopimarane classes, in addition to paraffins, methoxyphenols and carboxylic acids. Tetracyclic diterpenoids such as phyllocladane, kaurenol and kauranol were also present. The biomarker compositions are certainly typical for conifers and, given the absence of triterpenoids and diterpenoids such as ozic acid, angiosperms can be excluded as a botanical source. The absence of phenolic diterpenoids (ferruginol, totarol) and their derivatives excludes podocarpaceous affinities for the ambers from the Amazonas and Araripe basins. The fossil records of the embedding sediments (e.g. Araucariaceae pollen and leaves) support the proposal of an Araucariacae origin for these ambers, but Cupressaceae and Cheirolepidiaceae cannot be excluded. On the other hand, the presence of phyllocladane and kaurane derivatives is evidence for Araucariaceae or Podocarpaceae origins for the amber from the Recôncavo basin, but Cupressaceae cannot be excluded.  相似文献   

Geophysical characterization of the Ota–Vila Franca de Xira–Lisbon–Sesimbra fault zone, Portugal     

João Carvalho  Taha Rabeh  João Cabral  Fernando Carrilho  Jorge Miguel Miranda 《Geophysical Journal International》2008,174(2):567-584

  相似文献   

Geological and Isotopic Constraints on the Metallogenic Evolution of the Proterozoic Sediment-Hosted Pb-Zn (Ag) Deposits of Brazil   总被引：2，自引：0，他引：2  

Aroldo Misi  Sundaram S. Iyer  Colombo C.G. Tassinari  J. Richard Kyle  Carlos E.S. Coelho  Washington J.S. Franca-Rocha  Adriana S.R. Gomes  Ion A. Cunha  Ilson G. Carvalho 《Gondwana Research》1999,2(1):47

Integrated studies of seven Proterozoic sediment-hosted, Pb-Zn-Ag sulfide deposits of Brazil, permit the estimation of the age of the hosting sequence and the mineralization, the nature of the sulfur and metal sources, the temperature range of sulfide formation and the environment of deposition. These deposits can be classified into three groups, according to their ages. (a) Archean to Paleoproterozoic: the Boquira deposit, in Bahia state, consists of stratiform massive and disseminated sulfides hosted by parametamorphic sequences of grunnerite-cummingtonite+magnetite that represent a silicate facies of the Boquira Formation (BF). Lead isotope data of galena samples indicate a time span between 2.7 and 2.5 Ga for ore formation, in agreement with the stratigraphic position of the BF. The relatively heavy sulfur isotope compositions for the disseminated and stratiform sulfides (+8.3 to +12.8 ‰ CDT)suggest a sedimentary source for the sulfur. (b) Paleo to Mesoproterozoic: stratiform and stratabound sulfides in association with growth faults are present in the Canoas mine (Ribeira, in Paraná state) and in the Caboclo mineralization (Bahia state). They are hosted by calcsilicates and amphibolites in the Canoas deposit, whereas in the Caboclo area the mineralization is associated with hydrothermally altered dolarenites at the base of the 1.2 Ga Caboclo Formation. The interpreted Pb-Pb age of the Canoas mineralization is coeval with the 1.7 Ga host rocks. Sulfur isotopic data for Canoas sulfides (+1.2 to +16 ‰ CDT) suggest a sea water source for the sulfur. The range between −21.1 and +8.8 ‰ CDT for the Caboclo sulfides could suggest the action of bacterial reduction of seawater sulfates, but this interpretation is not conclusive. (c) Neoproterozoic: stratiform and stratabound sulfide deposits formed during the complex diagenetic history of the host carbonate rocks from the Morro Agudo (Bambui Group), Irecê and Nova Redenção (Una Group), yield heavy sulfur isotope values (+18.9 to +39.4 ‰ CDT). The uniform heavy isotope composition of the barites from these deposits (+25.1 to +40.9 ‰) reflect their origin from Neoproterozoic seawater sulfates. The late-stage, and most important, metallic concentrations represent sulfur scavenged from pre-existing sulfides or from direct reduction of evaporitic sulfate minerals. Lead isotope data from the Bambui Group suggest focused fluid circulation from diverse Proterozoic sediment sources, that probably was responsible for metal transport to the site of sulfide precipitation. (d) Late Proterozoic to Early Paleozoic: lead-zinc sulfides (+pyrite and chalcopyrite) of Santa Maria deposits, in Rio Grande do Sul, form the matrix of arkosic sandstones and conglomerates, and are closely associated with regional faults forming graben structures. Intermediate volcanic rocks are intercalated with the basal siliciclastic members. Lead isotope age of the mineralization (0.59 Ga) is coeval with the host rocks. Sulfur isotopic values between −3.6 and +4.1 are compatible with a deep source for the sulfur.Geological, petrographic and isotopic data of the deposits studied suggest that they were formed during periods of extensional tectonics. Growth faults or reactivated basement structures probably were responsible for localized circulation of metal-bearing fluids within the sedimentary sequences. Sulfides were formed by the reduction of sedimentary sulfates in most cases. Linear structures are important controls for sulfide concentration in these Proterozoic basins.  相似文献   

Metal concentrations, fluxes, inventories and chronologies in sediments from Sepetiba and Ribeira Bays: A comparative study     

Franciane de Carvalho Gomes  Jos Marcus Godoy  Maria Luiza D.P. Godoy  Zenildo Lara de Carvalho  Ricardo Tadeu Lopes  Joan Albert Sanchez-Cabeza  Luiz Drude de Lacerda  Julio Cesar Wasserman 《Marine pollution bulletin》2009,59(4-7):123

Three sediment cores were sampled at Sepetiba Bay and four cores at Ribeira Bay, Rio de Janeiro State, Brazil. Sediment accumulation rates and chronologies were obtained from ²¹⁰Pb activity-depth profiles. Sediment accumulation rates in Ribera Bay ranged from 1.2 mm y⁻¹ in the inner bay to 2.6 mm y⁻¹ close to its entrance. In Sepetiba Bay two sediment accumulation rates were observed: a lower rate of 0.35 cm y⁻¹ before the 1960s and 0.76 cm y⁻¹ since then. The cause of this change is due to the construction of the Santa Cecília impoundment (1955) that brings water from the Paraíba do Sul Basin into the Guandu River, which increased its flow from the original 20 m³ s⁻¹ to 160 m³ s⁻¹. Concentration of 44 elements was obtained by ICP-MS after total dissolution of samples from two selected cores. The relative differences between the concentrations of crustal elements, such as Al, Fe and Ti are only about 20% (p < 0.05). Cd and Zn are 15 and four times larger in Sepetiba Bay than in Ribeira Bay, respectively. Other major and minor elements show lower statistically significant differences. The enrichment factors and metal inventories show that Sepetiba Bay can be considered polluted with Bi, Cd, Cr, Cu, Sb and Zn. Particularly, Cd and Zn present concentrations three and four times higher than the Brazilian existing limits.  相似文献   

Evaluation of seismic risk and mitigation strategies for the existing building stock: application of LNECloss to the metropolitan area of Lisbon     

A. Campos Costa  M. L. Sousa  A. Carvalho  E. Coelho 《Bulletin of Earthquake Engineering》2010,8(1):119

Decisions to mitigate seismic risk require a consistent approach to evaluate the effects of future earthquakes on population, on civil engineering structures and infra- structures. The mathematical and probabilistic methods that are the support to those approaches are generally called Risk Analysis; in the particular case of seismic events and mitigation strategies it will be named Seismic Risk and Mitigation Analysis, SRMA. The paper will address the subject of estimating the seismic risk and evaluate mitigation strategies for the existing building stock of the metropolitan area of Lisbon by describing the methods and showing preliminary results obtained with LNECloss numerical tool. Even though such a sophisticated tool needs validation on some parameters to become more reliable, it is shown that it is possible to compare results of different mitigation strategies.  相似文献   

Assessing aquatic macrophyte community change through the integration of palaeolimnological and historical data at Loch Leven,Scotland   总被引：1，自引：0，他引：1  

Jorge Salgado  Carl Sayer  Laurence Carvalho  Thomas Davidson  Iain Gunn 《Journal of Paleolimnology》2010,43(1):191-204

Submerged macrophytes have a critical role in lake ecosystems affecting nutrient cycling, sediment stability, and community composition across multiple trophic levels. Consequently temporal changes in the composition of submerged plant populations can have profound ecological implications and key significance from the perspective of lake conservation. By focusing on macro-remains of aquatic macrophytes and extensive historical plant records spanning the last approximately 180 years, this study seeks to evaluate a combined historical-palaeolimnological approach for establishing pre-disturbance macrophytes communities in Loch Leven, Kinross, Scotland and to provide new information regarding temporal trends in its macrophyte vegetation as well as potential drivers of change. Some 81% of the species historically recorded for the core site (east side of St. Serf’s Island) were found as macro-remains. Potamogeton taxa were underrepresented, whereas remains of Elatine hexandra, a small species never recorded historically were found. The core sequence showed good agreement with known floristic changes including an early (pre- ca. 1850) loss of Isoetes lacustris and Lobelia dortmanna and a more recent (post-1910) shift to dominance by Potamogeton and Chara taxa associated with eutrophic conditions. A clear pattern in the relationship between macrofossil principal component analysis (PCA) and loss on ignition suggested a key control of sediment conditions on macrophyte community structure. In particular the major macrophyte community change of the mid-nineteenth century was concurrent with a substantial increase in organic matter, likely linked to a historic lake lowering (early 1830s) which would have beached the former gravel-sand shoreline leading to a much siltier lake littoral. Although recent monitoring data show signs of ecological recovery our study illustrates that Loch Leven remains a long way from its reference state as a lake with characteristic soft-water macrophytes. To achieve a full recovery, sediment properties would need to change in addition to nutrient reduction. Consequently restoration strategies will need to compromise between the desirability of achieving the pre-disturbance state and what is feasible and practicable. Our study shows the clear potential role of a combined palaeolimnological-historical approach for informing lake management decisions.  相似文献   

Characterization of a profile of residual soil from granite combining geological, geophysical and mechanical testing techniques     

A. Viana Da Fonseca  J. Carvalho  C. Ferreira  J. A. Santos  F. Almeida  E. Pereira  J. Feliciano  J. Grade  A. Oliveira 《Geotechnical and Geological Engineering》2006,24(5):1307-1348

This paper summarizes the results of an experimental site investigation and characterization survey, on a residual (saprolitic) soil from granite, in the framework of a research project led by the Faculty of Engineering of the University of Porto (FEUP). This project aims at characterizing these unusual soils in the context of the development of an International Prediction Event (Class A) on the behaviour of different types of piles. A very extensive site characterization campaign, including a large variety of in-situ tests and field methods, has been held. These investigations comprised the application of several geophysical borehole and surface methods, namely P- and S-wave seismic refraction, reflection, cross-hole (CH), down-hole (DH), electrical resistivity imaging and ground probing radar (GPR), as well as mechanical tests, namely SPT, CPT and DMT, among others. The site is geologically formed by an upper layer of heterogeneous residual granitic soil, overlaying rather weathered granite contacting a gneissic migmatite. Direct and indirect results from some of the referred surveys were compared between them and with some of the available geological and geotechnical information, namely those obtained from seismic, electrical and GPR profiles, conducted adjacent to three boreholes in which undisturbed soil samples were collected previously to geophysical data acquisition. In addition, a comprehensive laboratory testing program was carried out using the collected undisturbed samples. A discussion of the obtained results is hereby presented, giving emphasis to the correlations encountered between the different tests, specific of saprolitic soils with weak relic structures.  相似文献